Software giant Microsoft is to appeal a fine of €899m (£709m) imposed by the European Commission in February.
The fine was brought against Microsoft for non-compliance in paying a 2004 antitrust fine, taking the total amount the Commission had fined Microsoft to €1.68bn.
"Microsoft has filed an application with the European Court of First Instance to annul the European Commission's 27 February decision," Microsoft said on Monday. "We are filing this appeal in a constructive effort to seek clarity from the court. We will not be saying anything further."
A Commission spokesperson said on Monday that the body believed its earlier decision to be "legally sound".
The spokesperson declined to comment as to whether the Commission was surprised about Microsoft's decision to appeal, given the software giant's statement in February that the fine related to "past issues" and that the company was looking to the future.
"It's their right to appeal the decision," said the spokesperson. The 27 February fine was imposed by the Commission for failure to pay a €497m fine imposed in 2004.
"Microsoft was the first company in 50 years of EU competition policy that the Commission has had to fine for failure to comply with an antitrust decision," competition commissioner Neelie Kroes said in a statement at the time. "I hope that today's decision closes a dark chapter in Microsoft's record of non-compliance with the Commission's March 2004 decision."
In 2004, the Commission ruled that Microsoft had withheld workgroup server interoperability information from competitors, The Commission fined the software giant and ordering it to make the data available.